“U.S. Pt. No. 5,138,235 discloses a starting and operating circuit for an arc discharge lamp. The circuit comprises a DC power supply means coupled to AC input terminals, oscillator means coupled to said DC power supply to receive a DC voltage, oscillator staffing means and load means coupled to the output of the oscillator and including an inductor in series with the discharge lamp and a capacitor in parallel to the lamp. Upon switching on an AC power supply to the circuit the capacitor has a low impedance, an initial current through the inductor is high and a voltage across filamentary electrodes at ends of the lamp is high. With said latter voltage being sufficient high the lamp will ignite. Then the impedance of the load will decrease, which is reflected to the operation of the oscillator such that its oscillation frequency decreases from an ignition frequency to a lower normal operating frequency. In one example the ignition frequency is 46 kHz and the normal operating frequency is 25 kHz (according to electronic file of said document). This means a ratio between those frequencies is 1.84.”
U.S. Pat. No. 5,438,243 discloses an electronic ballast for instant start gas discharge lamps. The ballast differs from the circuit disclosed by U.S. Pat. No. 5,138,235 in that the oscillator, called inverter in U.S. Pat. No. 5,438,243, comprises at its output a transformer of which the secondary winding supplies several gas discharge lamps in series with series inductors and capacitors. The inverter comprises two switched resonating sections for increasing a resonating frequency to over 50 kHz of the inverter at normal operating of the lamps. According to the document (column 4 lines 33-36): “Increasing the frequency reduces the values of the transformer and the ballast inductor and capacitors. Increasing the frequency also improves the performance and reduces the cost of the ballast.”
U.S. Pat. No. 6,437,520 discloses an electronic ballast with cross-coupled outputs, comprising two inverters, of which each inverter provides a low voltage alternating current at an AC output of the other inverter. As an example, at ignition the frequency is 80 kHz and with normal operation the frequency is 40 kHz. This means a ratio between those frequencies is 2.